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Mystery cloud-like blobs over Mars baffle astronomers

In 2012, amateur astronomers spotted at least one unidentified object rising into the Martian sky. Could auroras, volcanoes or aliens be to blame?

By Jacob Aron

WE THINK we know our red neighbour pretty well. The first map of Mars was sketched 500 years ago, and we have sent more than 50 robot explorers to patrol the surface and watch it from orbit. Seven are on the case right this minute. When it comes to Mars, we are not easily surprised.

Hence the shock when, on 12 March 2012, amateur astronomers around the world noticed a strange blob rising from the planet’s southern hemisphere, soaring to 250 kilometres above the surface. Nearly three years later, the sighting still defies explanation.

The blob appeared only in the mornings and grew to around 1000 kilometres across in the following 11 days, even stretching a “finger” out into space. “I was really quite amazed that it was sticking out the side of the planet quite prominently,” says Damian Peach, who lives in Selsey, UK, and was one of the first to spot it.

Poor weather and other issues meant no one had their eye on Mars the following week, and by 2 April it seemed to have disappeared. Then on 6 April a second object of the same type emerged from the same spot and lasted another 10 days. It, too, has not been seen since.

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Now, in an attempt to pin down the blobs’ origins, Agustin Sánchez-Lavega of the University of the Basque Country, Bilbao, Spain, and colleagues including Peach, have dug out images of Mars from that period. In the end they amassed pictures from 18 observers equipped with a variety of small telescopes. The team also searched through old images taken by the Hubble Space Telescope and identified a similar object in 1997.

The team considered several possible explanations, each more exotic than the last. Despite their best efforts, though, they couldn’t come up with any that fitted known processes – and neither can anyone else (Nature, doi.org/z9j). “Frankly, I’m puzzled by the observations,” says Bruce Jakosky of the University of Colorado at Boulder, who leads NASA’s Mars-atmosphere-observing MAVEN mission. “I don’t understand how material can get that high and stay there for so long.”

Frankly, I’m puzzled. I don’t understand how material can get that high and stay there for so long

One clue is that the blobs seemed to appear at Mars’s terminator, the fuzzy line where night turns into day. That suggests the source might be a change in atmospheric temperature due to the morning sun. The team’s best guess is that the object is a cloud of frozen carbon dioxide and water particles condensing in the upper atmosphere.

If that’s the case, it would be unlike any cloud seen anywhere on Mars, or on Earth. Clouds on both planets are only ever seen at altitudes below 100 kilometres, which on Earth is the accepted height for the beginning of outer space. “If the phenomenon is a cloud, then the most similar phenomena on Earth will be the mesospheric clouds that form at 80 kilometres altitude on polar regions,” says Sánchez-Lavega.

With that in mind, thoughts have turned to other potential explanations. Charged particles from the sun interact with the Earth’s magnetic field to make the upper atmosphere glow – the phenomenon we call auroras. Mars’s magnetic field is weak and patchy in comparison, meaning auroras were first seen there when we had a spacecraft in place in 2005. That sighting was over a region tantalisingly close to the unexplained blobs.

The team calculate that the blobs could be auroras, but only if they are more than 1000 times brighter than Earth’s. That seems unlikely, especially since the sun wasn’t particularly active then.

What if a massive volcano were pumping material into the atmosphere? The blobs seemed to extend upwards from the surface, though it’s hard to determine this exactly given the quality of the images we have. But that wouldn’t explain why the blobs only appeared in the morning, says Sánchez-Lavega, and in any case we don’t know of any active volcanoes on Mars.

“You would think that something large enough to dump that much vapour in the atmosphere would be picked up,” says Nicholas Heavens of Hampton University in Virginia. A massive dust storm is also ruled out, as they normally don’t reach above 60 kilometres and the blob doesn’t carry Mars’s dusty red signature.

OK, now we’re getting really desperate. Could the explanation be biological? Whether there is life on Mars is one of the planet’s major mysteries (see “Three more martian Mysteries“), but any alien-hunters excited by the blobs should calm down, says Sánchez-Lavega&colon; “No life past or present [has been] detected so far on Mars, so it cannot be.” Heavens says there isn’t really enough data to rule either way, but it’s better to be cautious. “If there is no positive evidence, you should probably exclude something biological.”

What to do? Just wait and hope the object turns up again, although Peach thinks that the favourable conditions of 2012 may not reoccur for some time. “The season on Mars is very cloudy around that time of year, and that just happened to occur at opposition” – when Mars and Earth are aligned on the same side of the sun. That particular close combination won’t happen again for over a decade.

Perhaps one of our robot minions will be lucky. MAVEN’s orbit would have allowed it to fly through the blob, but the probe only reached Mars last year. “MAVEN should see something like this very easily if it occurred again, if we were at the right place at the right time,” says Jakosky. “I’ve given a heads-up to our science team, so they’ll be keeping an eye out for it.”

Three more martian Mysteries

Anyone there?

You can’t talk about Mars without talking about the possibility of life. The latest view, thanks to NASA’s Curiosity rover, is that the planet was definitely capable of hosting life in the past – but the jury is still out on whether microbes once thrived there. The ExoMars rover, launching in 2019, might be equipped to give a definitive answer.

Who dealt it?

A related mystery is figuring out the source of short-lived bursts of methane on Mars. Burping microbes are one possibility, but geological processes can also produce pockets of underground methane that might gradually seep out to the surface. The ExoMars Trace Gas Orbiter will be on the case when it launches in 2016.

Call that a moon?

Mars has the weirdest moons in the solar system. Phobos and Deimos are lumpy, misshapen rocks, and tiny compared with other planets’ spherical satellites. The moons might be captured asteroids shot out of the asteroid belt toward Mars by Jupiter’s gravity, or even chunks of Martian crust blasted off the surface by an ancient impact. A Russian mission to land on Phobos in 2011 was meant to bring samples, and answers, back to Earth, but a botched launch means we remain in the dark for now.

This article appeared in print under the headline “What’s flying over Mars…”